I have an idea of using ion ramjets in space. Since space is full of charged particles, it would be easy to pull in ions and accelerate them out the nozzle of a ramjet. All you would need are some electromagnets to suck in the ions and shoot them out the back. The only thing I don't know is the concentration of these ions in planetary space. I want to build an ion ramjet to test my theory. I also don't know of any gases I can ionize to test my idea. So here are my two questions:
-What are the concentrations of ions in planetary space?
-What are some (CHEAP, EASY TO OBTAIN) gases that can be ionized (and that will stay ionized)?